The cause of the birds’ death is under investigation, the Alberta Energy Regulator said. In the image, a great blue heron.

The Canadian province of Alberta’s Energy Regulator said Saturday it’s investigating reports of about 30 blue herons found dead at Syncrude Canada Mildred Lake oil sands mine site, north of Fort McMurray.

The agency said a Syncrude worker found one of the birds Wednesday, still alive, but the heron had to be euthanized. After the company searched the area, they found the rest of the birds dead in an abandoned run-off pond.

The regulator said that wildlife deterrent programs, including those at the Mildred Lake, are inspected regularly to make sure they're working following previous bird deaths at oil sands facilities.

In 2010, Syncrude was fined $2.3 million (Cdn$3 million) for negligence in the 2008 deaths of 1,600 ducks in a toxic waste pond, a case that fuelled international criticism and raised questions about the environmental impact of developing Canada's oil sands.

In November last year, 122 birds were killed after landing in three tailings ponds in the area, including one at Mildred Lake.

Authorities said it is too soon to know whether this new incident will result in charges.